This invention relates to a self-cleaning rotatable clamping device of the type used to clamp or hold-down a freight container to an underlying support platform, or a further container in order to form a stack of containers.
It is well known to use so-called xe2x80x9ctwistlok headsxe2x80x9d in clamping devices for freight containers, in which the corners (and optionally at other locations) of the container are provided with so-called xe2x80x9ccorner fittingsxe2x80x9d, and which are robust cast housings secured to the container structure and having a hollow interior which receives a clamping head of an underlying clamping device via an entrance opening in the housing.
In the case of spring loaded clamping heads, the head is normally spring-biassed to a clamping position, but is movable through approximately 90xc2x0 against the spring biassing by inter-engagement between the corner fitting and the head as the container is lowered into position, whereby the head is able to pass through the entrance opening and into the interior of the corner fitting. After the head is received within the corner fitting, it is then free to rotate under the spring biassing in order to resume its clamping position in which it holds down or clamps the corner fitting to the clamping device.
In more simple designs of freight container clamping device, the head is manually rotated between the clamping position and a release position (permitting movement of the head into or out of the housing depending upon whether loading or unloading of the container is taking place).
A clamping device for a freight container usually comprises a main housing, a vertical actuator shaft rotatably mounted in the housing, a twistlok or other clamping head secured to the upper end of the shaft, and usually a manually operated lever connected to the lower end of the shaft. In the case of a spring loaded head, the lever is operated only to move the head to a release position prior to unloading of a container, but for a non- spring loaded head the lever may be operated to adjust the head between the clamping and release positions during loading and unloading.
Regardless of the type of clamping device used, it is usual to provide a spring loaded detend which has the function of lightly maintaining the shaft in any one or more predetermined angular setting (corresponding to the clamping and/or the release of the head), and the detent may take the form of a compression spring which is housed in a diametrically extending slot formed in the shaft, and a pair of detent balls arranged one at each end of the spring and biassed outwardly into engagement with the cylindrical wall of the passage formed in the housing to receive the shaft.
Circumferentially spaced indentations (or, recesses) are formed in the cylindrical wall at angular locations corresponding to the required detent positions of the head, and when the shaft is actuated to move the head between its release and clamping positions, the balls roll and/or slide along a circular path of contact with the cylindrical wall until they come into registry with the indentations and are then spring-pressed into light holding or detent positions in the indentations.
The detent positions are not intended to lock the head in position, but to provide a light holding action for a temporary period when required.
In known arrangements, the actuator shaft has smooth slidable engagement with the cylindrical wall of the passage, but inevitably over a period of time there is ingress of dirt and grit into the annular space defined between the outer surface of the shaft and the inner surface of the cylindrical wall. In addition, repeated actuation of the shaft (and of the detent arrangement) will, over a period of time, generate wear in the engaging surfaces and which will form metal dust which remains trapped in the same annular space.
This build-up of material in the annular space increases the resistance to actuating movement of the shaft (and which may eventually become jammed in position) and also further increases the wearing action.
The invention therefore seeks, by simple means, to provide a self-cleaning effect, by enabling any dirt and other debris which is created in the region of the interface between the shaft and the cylindrical wall to be discharged during use of the clamping device.
According to the invention there is provided a rotatable clamping device of the type used to clamp a corner fitting of a freight container to an underlying support, and comprising:
a main housing defining an upright cylindrical passage in which an actuator shaft is rotatably mounted;
a clamping head secured to an upper end of the actuator shaft and rotatable with the shaft between a release position and a clamping position with respect to a corresponding corner fitting;
actuator means coupled with the shaft and operative to rotate the clamping head at least from the clamping position to the release position; and
a detent arrangement acting between the outer surface of the shaft and the inner wall surface of the cylindrical passage and operative to define a detent position and permit location of the shaft in at least one predetermined angular setting relative to the passage which corresponds to at least one of the release and clamping positions of the clamping head;
in which:
the detent arrangement comprises at least one recess formed in one surface of said shaft surface and said inner wall surface, and a resiliently biassed element pressed towards said one surface and engageable in said recess upon rotation of the shaft to said predetermined angular setting; and
a downwardly extending slot is formed in said one surface and communicates with said recess in order to form a means of gravity discharge of dirt/debris collected in the annular space between the outer surface of the shaft and the inner wall surface of said passage.
Therefore, in a clamping device of the invention, a detent arrangement is provided whose normal purpose is to define and then locate the shaft in the predetermined angular setting, but which also provides a self-cleaning function during actuation of the shaft, in that any dust, dirt, swarf etc. generated and/or collected in the annular space between the outer surface of the shaft and the inner wall surface of the passage can be discharged via the discharge slot.
This improves the working life of the clamping device, and eases the actuation of the shaft.
Preferably, the recess is formed in the inner wall surface of the passage, and the resiliently biassed element is housed in the shaft.
The resiliently biassed element may comprise a compression spring housed in a diametral slot extending through the shaft, and a ball and/or slidable element arranged at one end of the shaft and urged radially outwardly into contact with the passage wall. Then, upon rotation of the shaft, the ball or slidable element moves over the inner wall surface of the passage, and cleans it, as it moves into engagement with the recess.
If required, balls may be arranged one at each end of the compression spring.
The actuating means may comprise a simple actuator lever or handle, and which is operated in order to move the clamping head from the clamping position to the release position, in order to permit release of the clamping device from a corner fitting.
In a semi-automatic clamping device, a biassing spring, or other biassing means, may be provided in order to urge the clamping head to take up the clamping position, and therefore to restore the clamping head to the clamping position after entry of the clamping head into the corner fitting.